Pistons for internal combustion engines, or for compressors

ABSTRACT

A piston for an internal combustion engine or a compressor has a gudgeon pin bore of which a segment of the gudgeon pin bore wall is relieved on one side only of a plane which contains the axis of the gudgeon pin and is parallel to the piston axis.

United States Paten Hill et al. July 17, 1973 PISTONS FOR INTERNAL COMBUSTION ENGINES, OR FOR COMPRESSORS [56] References Cited [75] Inventors: Harold Taylor Hill, Sway, UNITED STATES PATENTS Hampshire; David Francis R26,764 1 1970 Packard et a1 92/187 Fl tch r-J n s, N Mllt n, H s. 2,387,634 10 1945 Anderson 92/187 both of England 2,388,363 11/1945 Moore 92/187 2,990,226 6/1961 Fan man 92/187 [73] Assignee: Wellworthy Limited, Hampshire, 3,006,698 10/1961 Dilv onh 1. 287/211 P England [22] Filed: Jan. 19, 1972 Primary Examiner-Irwin C. Cohen pp No 219,057 Att0rneyJohn A. Mawhmney [57] ABSTRACT [30] Foreign Apphcatlm] Priority Data A piston for an internal combustion engine or a com- Ffib. 9, 1971 Great Bl'ltalll 4,236/71 pressor has a g dg bore of a Segment f the gudgeon pin bore wall is relieved on one side only [52] US. Cl. 92/187 of a plane which contains the axis of the gudgwn pin III. Cl F16] and is parallel to the piston axis [58] Field of Search 92/187, 238; 308/4;

4 Claims, 3 Drawing Figures PATENIED JUL 1 71975 SHEET 1 BF 2 PATENTED JUL 1 7 I973 SHEET 2 OF 2 PISTONS FOR INTERNAL COMBUSTION ENGINES, OR FOR COMPRESSORS This invention relates to pistons for internal combustion engines, or for compressors.

In use, an internal combustion engine or compressor piston is periodically subjected to a high compressive load in the direction of the piston axis. This load acts upon the gudgeon pin, which in turn applies a load substantially perpendicular to both the piston axis and the axis of the gudgeon pin bore to the normally cylindrical walls of the gudgeon pin bore. These walls may thus become highly stressed, and may eventually crack. It is an object of the present invention to alleviate this problem.

According to the present invention, therefore, there is provided a piston for an internal combustion engine or a compressor wherein a segment of the otherwise cylindrical wall of the gudgeon pin bore is relieved on one side only of a plane which contains the axis of the gudgeon pin bore and is parallel to the piston axis.

Said one side is preferably adjacent the non-thrust side of the piston.

The invention will now be described, by way of nonlimitative example only, with reference to the accompanying drawings, of which:

FIG. 1 is a sectional view through the longitudinal axis of one embodiment of an internal combustion engine piston in accordance with the present invention;

FIG. 2 is a section on the line 2-2 of FIG. 1; and

FIG. 3 is a sectional view, similar to that shown in FIG. 2, of another embodiment of an internal combustion engine piston in accordance with the present invention.

The piston shown in FIGS. 1 and 2 is substantially cylindrical, and comprises a crown portion containing a combustion recess 12 in its upper surface. The cylindrical surface of the crown portion 10 contains a plurality of circumferential ring grooves 14. An openended skirt 16 extends downwardly from the crown portion 10 and is preferably integral therewith. Two spaced-apart gudgeon pin bosses 18, also integral with the crown portion 10, depend from diametrically opposed regions thereof.

The crown portion 10, the skirt 16 and the gudgeon pin bosses 18 are conveniently cast in one piece from aluminium or an aluminium alloy.

Each of the gudgeon pin bosses 18 is provided with a substantially cylindrical bore 20, as will hereinafter be described. The bores 20 are coaxially aligned and together constitute a gudgeon pin bore: the axis of the gudgeon pin bore 20 is indicated at 21, and it may intersect the piston axis 22.

In use, the piston is reciprocably mounted in the cylinder (not shown) of an internal combustion engine, and is joined to the crankshaft (not shown) of the engine via a cylindrical gudgeon pin 23 and a connecting rod (not shown). The gudgeon pin 23 is journalled in the gudgeon pin bore 20, while the upper end of the connecting rod is journalled around the gudgeon pin 23 between the gudgeon pin bosses 18. The lower end of the connecting rod is journalled upon an eccentric crank pin on the crankshaft.

When the charge of fuel and air in the space in the cylinder above the piston is ignited and. combustion takes place, the piston is driven downwardly in the direction of its axis 22, and as a result is subjected to a high compressive load along its axis 22. Assuming that the piston shown in FIG. 1 drives its crankshaft, whose axis is perpendicular to the plane of FIG. 1, in a clockwise direction, then the left-hand side 24 of the skirt 16, as viewed in FIG. 1, is the thrust face thereof, while the right-hand side 25 is the non-thrust face thereof.

The compressive load on the piston is transferred, via the gudgeon pin bosses 18, to the gudgeon pin 23, which in turn applies a transverse load (i.e., perpendicular to the axes 21 and 22) to the walls of the gudgeon pin bore 20. This transverse load produces distortion of the gudgeon pin bosses l8 and the gudgeon pin 23. The distortion is particularly pronounced with lightweight hollow gudgeon pins such as that illustrated, since they tend to ovalise under the compressive load. Additionally, the wall of the cylinder exerts a considerable force on the thrust face 24 of the skirt 1.6, which force is also transferred to the gudgeon pin 23. The major axis of the ovalised shape adopted under load by the gudgeon pin 23 may therefore be slightly inclined to a line perpendicular to the piston axis 22 and the axis 21 of the gudgeon pin bore 20, the inclination being upwards from left to right as viewed in FIG. 1.

In order to prevent overstressing of the walls of the gudgeon-pin bore 20, a segment 26 of the otherwise cylindrical wall is relieved on one side only of a plane which contains the axis 21 of the gudgeon pin bore 20 and is parallel to the piston axis 22. This relieved portion provides space for the major axis of the ovalised shape of the gudgeon pin, and thereby reduces the tendency of the piston to crack upwards from the top of the gudgeon pin bore 20 towards the crown portion 10 of the piston. In the embodiment of the invention illustrated in FIGS. 1 and 2, the relieved segment 26 is nearer to the non-thrust face 25 of the skirt 16 than to the thrust face 24, and extends over an angle of about 80. The angular midpoint of the relieved segment 26 is inclined towards the crown portion 10 of the piston from the normal to the axes 21 and 22 by about 30", so that the relieved segment 26 is nearer to the top of the gudgeon pin bore 20 than to the bottom thereof.

The amount of the relief 26 is substantially constant in the direction of the axis 22 of the gudgeon pin bore 20, as shown in FIG. 2. The relief 26 may conveniently be produced by means of a milling cutter, set to a diameter slightly smaller than that of the bore 20 and slightly offset from the axis 21.

Gudgeon pins also tend to curve slightly under the influence of the loads applied to their end regions by the gudgeon pin bosses and the oppositely directed load applied to their centre region by the connecting rod. This curvature further stresses the gudgeon pin bore, the effect being greatest in the portions of the bore closest to the piston axis.

This further stress is reduced in the embodiment of the invention illustrated in FIG. 3. In FIG. 3, where parts similar to those shown in FIGS. 1 and 2 are indicated by the same reference numerals with the suffix a, it can be seen that the amount of the relief 26a, in the respective portions of the gudgeon pin bore 20a, in each gudgeon pin boss 18a increases, axially of each portion of the bore 20a, towards the axis 22a of the piston. The relief 260 may conveniently be produced, from the outside of the piston, by means of a milling cutter set to a diameter slightly smaller than that of the bore 20 and inclined at a small angle, typically 1, to the axis 21.

We have found that the provision of a relieved segment such as 26 or 26a in the wall of the gudgeon pin bore or 20a, on one side only of the plane which contains the axis of the bore and is parallel to the piston axis, substantially relieves the crack-forming stresses to which the bore is subjected by the gudgeon pin 23 or 23a. Further, the provision of the relieved segment on one side only of said plane is simpler and more economical than, for example, providing respective relieved segments on both sides of the plane, and in addition can give better location of the gudgeon pin under side load conditions.

It will be appreciated that several modifications can be made to the described embodiments of the invention. For example, the relieved segments 26 or 26a could be symmetrically positioned between the top and bottom of their respective gudgeon pin bores, or they could be on the other side of the plane which contains the axis of the gudgeon pin bore and is parallel to the piston axis (i.e., the side adjacent the thrust face 24 or 24a, of the skirt l6-or 1641). Further, the gudgeon pin bores of pistons other than the examples specifically described can be relieved in accordance with the present invention, for example pistons in which the axis of the gudgeon pin bore is slightly offset from the piston axis.

What we claim is:

1. In a piston for an internal combustion engine or a compressor, a crown portion having an upper surface, a cylindrical skirt depending from the crown portion and having diametrically opposing thrust and nonthrust sides and radially aligned gudgeon pin bosses, each of said bosses being formed with a substantially cylindrical bore in between said thrust and non-thrust sides with the bores being coaxially aligned and in which a cylindrical gudgeon pin is joumalled, a segment of the otherwise cylindrical walls of the gudgeon pin bores on the non-thrust side is relieved, the greater part of the relieved segments is on the crown side of a plane through the gudgeon pin axis and normal to the piston axis, the remainder of the bores in the bosses having a truly circular configuration.

2. A piston, as claimed in claim 1, in which the relieved segment of the wall extends over an angle of between 60 and 3. The piston of claim 1 wherein the amount of the relief is substantially constant in the direction of the axis of the gudgeon pin bore.

4. The piston of claim 1 wherein the amount of the relief increases axially thereof towards the axis of the piston. 

1. In a piston for an internal combustion engine or a compressor, a crown portion having an upper surface, a cylindrical skirt depending from the crown portion and having diametrically opposing thrust and non-thrust sides and radially aligned gudgeon pin bosses, each of said bosses being formed with a substantially cylindrical bore in between said thrust and nonthrust sides with the bores being coaxially aligned and in which a cylindrical gudgeon pin is journalled, a segment of the otherwise cylindrical walls of the gudgeon pin bores on the nonthrust side is relieved, the greater part of the relieved segments is on the crown side of a plane through the gudgeon pin axis and normal to the piston axis, the remainder of the bores in the bosses having a truly circular configuration.
 2. A piston, as claimed in claim 1, in which the relieved segment of the wall extends over an angle of between 60* and 80*.
 3. The piston of claim 1 wherein the amount of the relief is substantially constant in the direction of the axis of the gudgeon pin bore.
 4. The piston of claim 1 wherein the amount of the relief increases axially thereof towards the axis of the piston. 